1. Field of the Invention
This invention relates to a semiconductor light emitting device.
2. Background Art
The semiconductor light emitting device, which emits mixed color of blue light from a nitride semiconductor light emitting element and yellow light obtained through wavelength conversion by phosphors, is finding wide application in displays, illuminations, and display backlights.
The semiconductor light emitting element includes a quantum well structure made of compound semiconductor thin films. It is not easy to control the composition and thickness of a heterojunction of compound semiconductor thin films having a thickness of approximately several nm. Hence the emission wavelength of a semiconductor light emitting element has a certain distribution.
On the other hand, the excitation spectrum of phosphors depends on wavelength. Consequently, if the emission wavelength of a semiconductor light emitting element varies several nm, the excitation intensity of phosphors also varies accordingly, changing the chromaticity of the mixed color.
JP-A 2005-252250 (kokai) discloses a light emitting device using an LED (light emitting diode) or LD (laser diode) with a peak wavelength of 380 to 410 nm as an excitation light source. In this device, despite some shift in its emission wavelength, the emission intensity of the red phosphor is not affected, keeping not only the brightness, but also the balance of mixing with blue and green phosphor.